Enhanced steel catenary riser system

Abstract

A riser arrangement increases the stability and/or decreases sensitivity to vortex induced vibration of risers of a riser system including steel tubular lines, SCRIBS and flexible hose risers leading to a floating storage/production vessel. A cross-link is placed between two or more steel tubular lines in order to enhance the stability of the riser system. Devices are coupled to the steel tubular lines for increasing their tension in order to increase the natural frequency of vibration in order to reduce sensitivity to vortex induced vibration.

What is claimed is: 
     
       1. An improved riser arrangement for a moored floating facility, the arrangement including a plurality of risers, each of which provides a fluid flow path between a seabed position and the floating facility in the sea, where each riser includes, a steel catenary riser which extends from a first end at a seabed position to a second end at a submerged depth position in the sea, said steel catenary riser having a catenary shape between said seabed position at said first end and said submerged depth position at said second end,   a flexible riser coupled at one end to said second end of said steel catenary riser to form a fluid flow path from said seabed position to an opposite end of said flexible riser, said opposite end of said flexible riser being coupled to said floating facility, and   a submerged steel catenary riser interface buoy positioned at said submerged depth position which supports said steel catenary riser and said flexible riser at said submerged depth position, where each steel catenary riser interface buoy for a riser is independent of each other steel catenary riser interface buoy for any other riser of said plurality of risers,   said improved riser arrangement including an improvement which comprises, a cross-link positioned between and coupled to at least two of said steel catenary risers, said cross-link thereby enhancing stability of said steel catenary risers.     
     
     
       2. The improved riser arrangement of claim 1 wherein said cross-link is a cable. 
     
     
       3. The improved riser arrangement of claim 1 wherein said cross-link is a beam. 
     
     
       4. The improved riser arrangement of claim 1 wherein said cross-link is a structure, arranged and designed for both tension and compression loads. 
     
     
       5. The improved riser arrangement of claim 4 wherein said structure is a triangular shaped structure, said structure leaving a first side of which extends in a perpendicular direction to and is connected to said at least two steel catenary risers, a second side which extends along and is connected to one of said at least two steel catenary risers, and a third side which forms the hypotenuse of a triangular shape of said triangular shaped structure. 
     
     
       6. The improved riser arrangement of claim 1 wherein said each of said plurality of steel catenary risers has a cross-link provided to another steel catenary riser in said plurality of steel catenary risers. 
     
     
       7. The improved riser arrangement of claim 1 wherein certain risers of said plurality of risers are import risers and certain other risers of said plurality of risers are export risers, and the improvement further comprises, one or more cross-links positioned between steel catenary risers of said import risers, and   one or more cross-links positioned between steel catenary risers of said export risers, and   wherein cross-linking of said import risers is independent of cross-links of said export risers.   
     
     
       8. The improved riser arrangement of claim 1 wherein, said cross-link is positioned between said at least two of said steel catenary risers at a level at said steel catenary riser interface buoys.   
     
     
       9. The improved arrangement of claim 8 further comprising, at least another cross-link positioned between said at least two of said steel catenary risers at a level below said steel catenary riser interface buoys.   
     
     
       10. The improved riser arrangement of claim 1 wherein, said cross-link is positioned between said at least two of said steel catenary risers at a level below said steel catenary riser interface buoys.   
     
     
       11. An improved riser arrangement for a moored floating facility in the sea, the arrangement including a plurality of risers, each of which provides a fluid flow path between a seabed location and the floating facility, where each riser includes, a tubular line which extends from said seabed location at a first end to a submerged depth position at a second end in the sea,   a flexible hose riser coupled at one end to said second end of said tubular line to form a fluid flow path from said seabed location to an opposite end of said flexible hose riser, said opposite end of said flexible hose riser being coupled to said floating facility, and   a submerged interface buoy positioned at said submerged depth position which supports said tubular line and said flexible hose riser at said submerged depth position, where each submerged interface buoy for a riser of said plurality of risers is independent of each other submerged interface buoy for any other riser,   said arrangement including an improvement which comprises, a cross-link positioned between at least two of said tubular lines, said cross-link enhancing stability of said tubular lines, and   a first line connected to a first of said at least two of said tubular lines at a first securement position and having a first anchor connected to an opposite end of said first line and extending to the seabed, and   a second line connected to a second of said at least two of said tubular lines at a second securement position and having a second anchor connected to an opposite end of said secured line and extending to the seabed, said first and second lines and said first and second anchors being arranged and designed to increase the tension in said tubular lines between said first and second securement positions and said submerged interface buoy of each of said at least two of said tubular line.